I. Field of Invention
The present invention generally concerns the field of microfluidic devices. More particularly, the present invention concerns a method and an arrangement for reducing noise in a substance raw data image containing noise. The present invention also relates to a method and an arrangement for determining a measure of at least one substance. The substance raw data image has been obtained from a search area that comprises a detection area associated with a detection microcavity that is part of a microchannel structure of a microfluidic device detectable signals.
The substance raw data image reflects from a substance that is present in the detection microcavity after one or more liquid aliquots have been processed through the microchannel structure that comprises the detection microcavity.
II. Related Art
All patents and patent applications cited in this specification are incorporated by reference in their entirety.
A. Background Publications
Detector arrangements for measuring radiation signals from individual detection areas on a circular substrate have been described in a number of previous publications. See for instance: EP 392475 (Idemitsu Petrochemical Co, Yamaji Kazutaka et al.) U.S. Pat. No. 5,994,150 (Imation Corp, Challener et al.), U.S. Pat. No. 5,892,577 (The University Court of the University of Glasgow, Gordon), WO 9721090 (Gamera, Mian et al.), Duffy et al., “Microfabricated Centrifugal Microfluidic systems: Characterization and multiple Enzymatic Assays” (Anal. Chem. 71 (1999) 4669–4678), WO 0040857 (Amersham Pharmacia Biotech AB, Björkesten et al.)
B. Background Technology and Problems
The present invention belongs to the field of miniaturization of processes which comprise sample treatment, assay protocols, chemical and/or biochemical synthesis etc., within medicine, chemistry, biochemistry, molecular biology and the like. At present one important goal within this field is to reduce the costs for these processes, for instance to reduce the amount of reagents needed per assay, reduce time per assay, etc. One route has been to increase the degree of parallelity, for instance by integrating as many as possible of similar process runs in one and the same device in order to carry out all the runs in parallel. At present, large numbers of research groups and companies are involved in developing technology that will solve the numerous problems encountered.
One problem is related to the optimal way of configuring the detector in relation to the microdevice used for performing the processes while maintaining an acceptable sensitivity and reproducibility. This problem may become particularly pronounced if the measuring step is performed by continuously moving the detector unit and the detection areas of a microfluidic device relative to each other during the measurement operation.
Another problem arises if the microfluidic device is in the form of a disc which is skewed because then it becomes difficult to maintain the optical focus in the right position relative to the detection areas. Without proper arrangement skewed discs will reduce sensitivity. This problem in particular applies to discs made of plastic material.
Another problem is related to maintaining an acceptable sensitivity and reproducibility when changing sample volumes from the μl-range to the nl-range and performing the process protocols with a high degree of parallelity within the same device. The inventors have found that under these circumstances the materials from which the microfluidic devices are fabricated and the various treatments during the manufacturing and conditioning of the devices easily introduce signal artifacts that are of the same kind and of comparable or larger size as the desired signals.
During recent years it has become popular to fabricate microfluidic devices in plastic material. This kind of material is typically highly fluorescent (“auto-fluorescent”) with emission wavelengths covering most of the wavelengths normally utilized in fluorescent measurements. Compared to microtitre wells and other uncovered microstructures the problem becomes more severe for the kind of covered microchannel structures used in the present invention, because the exciting and emitted radiation has to pass through plastic material. For transparent plastic material there is also a problem with “cross-talks” between the detection area/detection microcavities. Similar problems may also be at hand for spectroscopic methods in which the radiation to be measured is created within the detection microcavity (for instance chemiluminescence, bioluminescence, etc.,).
A more recent problem relates to the fact that the present assignee recently has managed to control the liquid flow in microfluidic devices containing a plurality of microchannel structures in such a way that the inter-channel variation for a device with respect to flow becomes insignificant. This progress has enabled the assignee to quantify with a low inter-assay variation and a high sensitivity analytes, such as antigens, in the subfemtomole range in nl-volumes by carrying out the solid phase reaction of a heterogeneous sandwich immunoassay under flow conditions in small columns (nl-columns). This has raised the question about measuring the amount of an affinity complex such as an immune complex as a function of position along the flow direction in a column. See WO 02075312 (Gyros AB) and assignee's poster presented on Sep. 17, 2001 at Proteomic Forum Sep. 16–19, 2001, Munich, Germany.